The story begins when the Crown Prince falls into the water and is rescued by her sworn enemy, the Emperor's other son. In the confusion, she touches something.
Yan Qiao: So this is what Mother meant when she said my brother and I were different.
Yan Zheng: My younger brother is quite handsome.
Later...
Yan Qiao: My brother keeps staring at me. He must be trying to expose my secret identity as a girl and strip me of my position as Crown Prince. I'm terrified!!
Yan Zheng: I think I might be gay.
Key points: Disguised as a man, no blood relation.
A fake Crown Prince who only wants to keep her secret identity hidden VS a straight man who thinks he's been turned gay